This invention relates to an induction system for an internal combustion engine that insures smooth running and minimizing pollutants under low load operating conditions.
Generally speaking, when an internal combustion engine is operated under low load, that is, with the throttle closed or nearly closed, for example at low speed, under low load, and during coasting, starting and idling operations, the efficiency of charging the air fuel mixture into the combustion chamber is so low that the speed of flame propagation is reduced to the point that combustion is unstable. For this reason, the thermal efficiency of an engine under these conditions is low, and smooth running is impossible due to resulting surges. Moreover, there is the defect that such incomplete combustion components as carbon monoxide, oxides of nitrogen and unburned hydrocarbons will be created in the exhaust.
Accordingly, recently methods have been used wherein a suitable turbulence is created in the combustion chamber for the purpose of increasing the propagation speed of the flame. There are two principal methods for creating this turbulence. One provides turbulence by "squish" of the piston during the latter portion of the compression stroke, and the other is a method wherein swirling flow in a tangential direction is imparted to the air/fuel mixture sucked into the combustion chamber by providing a shroud on the intake valve. However, with the squish method, unburned hydrocarbons are created in the squish region and are discharged in the exhaust. In the latter method, the shroud decreases the intake efficiency during high speed operation. Therefore, these methods are impractical.